Integrated circuits such as DRAMs are often placed in electronic systems that are less than ideal from an electrical noise standpoint. Noise on the DRAM inputs can cause internal misfiring and malfunction of the circuit. General practice is to assume that systems will always be noisy, and that the DRAM input should be modified to operate properly in spite of the noise.
Negative transitions on some DRAM input signals (such as an address strobe, for example) are critical, since a mistriggered strobe can begin an accidental access cycle within the DRAM, possibly altering stored data.
A well known method to reduce DRAM noise sensitivity is to run an input through a Schmitt type input buffer internal to the chip.